Substrate processing systems include a process chamber having a processing volume where a substrate may be disposed on a substrate support. One or more process gases may be flowed into the processing volume to process the substrate. Typically, in such systems, chamber pressure and process gas flow are controlled separately. For example, gas flow rates are set by flow controllers, such as mass flow controllers or the like. Similarly, pressure levels are set at an exhaust valve from the chamber, such as a throttle valve or the like. Flow rates can then be modified after pressure levels are set to adjust for residence time effects in the processing volume. In addition, when switching between processes at different flow rates and/or chamber pressures, substrate processing can be slowed while waiting for the system to stabilize at the second flow rate and/or chamber pressure.
Thus, the inventors have provided improved methods and apparatus for processing substrates.